Add ansi theme to replace ansi-light and ansi-dark

This combines ansi-light and ansi-dark into a single theme that works
with both light and dark backgrounds. Instead of specifying white/black,
the ansi theme uses the terminal's default foreground/background color
by setting alpha=01, i.e. #00000001. This is in addition to the alpha=00
encoding where red contains an ANSI color palette number.

Now, `--theme ansi-light` and `--theme ansi-dark` will print a
deprecation notice and use ansi instead (unless the user has a custom
theme named ansi-light or ansi-dark, which would take precedence).

src/assets.rs

@@ -189,6 +189,15 @@ impl HighlightingAssets {
         match self.theme_set.themes.get(theme) {
             Some(theme) => theme,
             None => {
+                if theme == "ansi-light" || theme == "ansi-dark" {
+                    use ansi_term::Colour::Yellow;
+                    eprintln!(
+                        "{}: Theme '{}' is deprecated, using 'ansi' instead.",
+                        Yellow.paint("[bat warning]"),
+                        theme
+                    );
+                    return self.get_theme("ansi");
+                }
                 if theme != "" {
                     use ansi_term::Colour::Yellow;
                     eprintln!(

src/printer.rs

@@ -448,7 +448,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                 if text.len() != text_trimmed.len() {
                     if let Some(background_color) = background_color {
                         let mut ansi_style = Style::default();
-                        ansi_style.background = Some(to_ansi_color(background_color, true_color));
+                        ansi_style.background = to_ansi_color(background_color, true_color);
                         let width = if cursor_total <= cursor_max {
                             cursor_max - cursor_total + 1
                         } else {
@@ -589,8 +589,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
 
             if let Some(background_color) = background_color {
                 let mut ansi_style = Style::default();
-                ansi_style.background =
-                    Some(to_ansi_color(background_color, self.config.true_color));
+                ansi_style.background = to_ansi_color(background_color, self.config.true_color);
 
                 write!(
                     handle,
@@ -624,20 +623,27 @@ impl Colors {
     }
 
     fn colored(theme: &Theme, true_color: bool) -> Self {
-        let gutter_color = theme
-            .settings
-            .gutter_foreground
-            .map(|c| to_ansi_color(c, true_color))
-            .unwrap_or(Fixed(DEFAULT_GUTTER_COLOR));
+        let gutter_style = Style {
+            foreground: match theme.settings.gutter_foreground {
+                // If the theme provides a gutter foreground color, use it.
+                // Note: It might be the special value #00000001, in which case
+                // to_ansi_color returns None and we use an empty Style
+                // (resulting in the terminal's default foreground color).
+                Some(c) => to_ansi_color(c, true_color),
+                // Otherwise, use a specific fallback color.
+                None => Some(Fixed(DEFAULT_GUTTER_COLOR)),
+            },
+            ..Style::default()
+        };
 
         Colors {
-            grid: gutter_color.normal(),
-            rule: gutter_color.normal(),
+            grid: gutter_style,
+            rule: gutter_style,
             filename: Style::new().bold(),
             git_added: Green.normal(),
             git_removed: Red.normal(),
             git_modified: Yellow.normal(),
-            line_number: gutter_color.normal(),
+            line_number: gutter_style,
         }
     }
 }

src/terminal.rs

@@ -3,13 +3,13 @@ use ansi_term::{self, Style};
 
 use syntect::highlighting::{self, FontStyle};
 
-pub fn to_ansi_color(color: highlighting::Color, true_color: bool) -> ansi_term::Color {
+pub fn to_ansi_color(color: highlighting::Color, true_color: bool) -> Option<ansi_term::Color> {
     if color.a == 0 {
         // Themes can specify one of the user-configurable terminal colors by
         // encoding them as #RRGGBBAA with AA set to 00 (transparent) and RR set
-        // to the 8-bit color palette number. The built-in themes ansi-light,
-        // ansi-dark, base16, and base16-256 use this.
-        match color.r {
+        // to the 8-bit color palette number. The built-in themes ansi, base16,
+        // and base16-256 use this.
+        Some(match color.r {
             // For the first 8 colors, use the Color enum to produce ANSI escape
             // sequences using codes 30-37 (foreground) and 40-47 (background).
             // For example, red foreground is \x1b[31m. This works on terminals
@@ -31,11 +31,18 @@ pub fn to_ansi_color(color: highlighting::Color, true_color: bool) -> ansi_term:
             // 90-97 (foreground) and 100-107 (background), we should use those
             // for values 0x08 to 0x0f and only use Fixed for 0x10 to 0xff.
             n => Fixed(n),
-        }
+        })
+    } else if color.a == 1 {
+        // Themes can specify the terminal's default foreground/background color
+        // (i.e. no escape sequence) using the encoding #RRGGBBAA with AA set to
+        // 01. The built-in theme ansi uses this.
+        None
     } else if true_color {
-        RGB(color.r, color.g, color.b)
+        Some(RGB(color.r, color.g, color.b))
     } else {
-        Fixed(ansi_colours::ansi256_from_rgb((color.r, color.g, color.b)))
+        Some(Fixed(ansi_colours::ansi256_from_rgb((
+            color.r, color.g, color.b,
+        ))))
     }
 }
 
@@ -54,7 +61,10 @@ pub fn as_terminal_escaped(
     let mut style = if !colored {
         Style::default()
     } else {
-        let mut color = Style::from(to_ansi_color(style.foreground, true_color));
+        let mut color = Style {
+            foreground: to_ansi_color(style.foreground, true_color),
+            ..Style::default()
+        };
         if style.font_style.contains(FontStyle::BOLD) {
             color = color.bold();
         }
@@ -67,6 +77,6 @@ pub fn as_terminal_escaped(
         color
     };
 
-    style.background = background_color.map(|c| to_ansi_color(c, true_color));
+    style.background = background_color.and_then(|c| to_ansi_color(c, true_color));
     style.paint(text).to_string()
 }